docs: redirect /training/lerobot to the LeRobot integration page

Production served the same LeRobot page at /training/lerobot and
/integrations/lerobotdataset. Only the integrations page carries over, so
the old Training URL now redirects to it instead of returning 404.

docs/web/docs.json

@@ -139,6 +139,10 @@
       "source": "/training",
       "destination": "/training/data-loading"
     },
+    {
+      "source": "/training/lerobot",
+      "destination": "/integrations/lerobotdataset"
+    },
     {
       "source": "/build-with-ai-agents",
       "destination": "/basics/agentic-skills"